<!DOCTYPE html>
<html>
  <svg width="200" height="200">
    <defs>
      <mask id="mask1" x="0" y="0" width="100" height="100" >
        <circle cx="100" cy="100" r="50" style="stroke:none; fill: #ffffff"/>
      </mask>
    </defs>
    <rect id="drawPath" x="50" y="50" width="100" height="100" fill="blue" stroke="blue" mask="url(#mask1)"/>
  </svg>
</html>
